Free radical initiator delivery system

ABSTRACT

This invention relates to an improved polymerization free radical initiator delivery system for the polymerization of monomers containing olefinic unsaturation and to the preparation of the initiator which comprises dissolving a water insoluble free radical initiator and an excess amount of the polymeric product of the reaction in a mutual organic solvent having a boiling point below 140° C., in the presence of between about 1.0 and 100 wt. % of a surfactant based on weight of initiator and mixing the resulting solution to achieve uniform molecular distribution of initiator and polymer molecules in the surfactant/solvent mixture; removing the solvent to provide coprecipitated initiator/polymer microparticles and then diluting the coprecipitated microparticles with water under vigorous agitation to form a microparticle emulsion of low viscosity which is suitable as the initiator feed for contact with monomer in a polymerization reaction.

This application is a continuation-in-part of patent application Ser.No. 08/44,520 and Ser. No. 08/44,136, both filed Apr. 8, 1993, now U.S.Pat. Nos. 5,270,271 and 5,362,698, respectively, for inventors Waldo DeThomas and Kolazi S. Narayanan and assigned to ISP Investments Inc.

A major difficulty encountered with many polymerization initiators, suchas the peroxy and azo initiators, is their insolubility in reactionmedia. In carrying out polymerizations, particularly in thosepolymerizations which employ continuous or timed addition, theseinitiators must be solubilized in order to be effective. Some processeshave used predissolution of initiator in mineral spirits or otherorganic solvents; however, these additives cause product qualityproblems which are not easily rectified. To overcome this difficulty,predissolution of the initiator in monomer has been employed, but thissolution leads to other difficulties involving highly reactive vinylmonomers, such as vinyl lactams, vinyl acetate, maleic anhydride,acrylates and the like, which rapidly polymerize and cause polymerplugging in the pumps, valves and feed lines of the process unless closetemperature control and other reaction parameters are closelymaintained.

The initiator feed preparation disclosed in U.S. Pat. No. 3,862,915suggests suspending crystalline azo type initiators in an 0.5-30%aqueous solution of polymer. However, the initiator feed prepared bythis method has not found general acceptance since such suspensions arerelatively unstable and the presence of free polymeric product has thetendency toward early termination of the desired monomericpolymerization reaction. Also the initiator crystals in the suspensionare not employed at maximum efficiency since the crystalline size doesnot approach microcrystallization which is desired for higher efficacy.

Accordingly, it is an object of the present invention to overcome theabove difficulties by providing an efficient, commercially feasible freeradical initiator delivery system for homo- and co-polymerization ofolefinic monomers.

Another object of this invention is to provide a highly stable initiatorfeed in liquid form which avoids the presence of any extraneous solventor diluent in the polymerization reaction.

These and other objects will become apparent from the followingdescription and disclosure.

THE INVENTION

In accordance with this invention, there is provided an emulsifiedpolymer/free radical initiator delivery system for the polymerization ofmonomers containing olefinic unsaturation which is prepared bydissolving a water insoluble free radical initiator and an excess.amount of a polymeric product of the polymerization reaction in amutual organic solvent having a boiling point below 140° C., optionallyin the presence of between about 1.0 and about 100 wt. % of asurfactant, based on weight of initiator; agitating the resultingsolution to obtain uniform distribution of polymer and initiatormolecules in the solvent mixture; removing the solvent to provide acoprecipitated, solid mixture of initiator and polymer in the form ofmicroparticles of between about 0.01 and about 100 micron size and thendiluting the coprecipitated microparticles with water under vigorousagitation to form a stable microemulsion which is suitable as a premixedinitiator feed for contact with monomer in the polymerization reaction.

Any of the various water insoluble free radical initiators, particularlythe solid initiators, can be employed as the initiator feed compositionin the above process. Examples of suitable initiators include the freeradical peroxy and azo type compounds, such as azodiisobutyronitrile(VAZO-64), azodiisovaleronitrile (VAZO-52), dimethylazodiisobutyrate(WAKO 601), 2,2'-azobis(isobutyronitrile),2,2'-azobis(N,N'-dimethyleneisobutyramidine)dihydrochloride,2,2'-azobis(2-amidinopropane)dihydrochloride,2,2'-azobis(N,N'-dimethyleneisobutyramidine),1,1'-azobis(1-cyclohexanecarbo-nitrile), 4,4'-azobis(4-cyanopentanoicacid), 2,2'-azobis(isobutyramide) dihydrate,2,2'-azobis(2-methylpropane), 2,2'-azobis(2-methylbutyronitrile), VAZO67, cyanopentanoic acid, the peroxy pivalates, dodecylbenzene peroxide,benzoyl peroxide, di-t-butyl hydroperoxide, t-butyl peracetate, acetylperoxide, dicumyl peroxide, cumyl hydroperoxide, dimethylbis(butylperoxy) hexane and generally any of the solid or liquidoil-soluble free radical initiators conveniently employed forpolymerizations involving monomers containing olefinic unsaturation.

In the above emulsification process, the surfactant may be introducedseparately, with the free radical initiator, or with the mutual solventor can be omitted from the free radical delivery system and insteadintroduced directly into the monomeric polymerization mixture. However,it is preferred to include surfactant in the delivery system for theadditional improvement realized thereby. Specifically, the presence ofsurfactant provides for improved homogeneous distribution of the fineparticles in the emulsion.

The surfactant added to the delivery system is employed in an amountbetween about 1.0 and about 100 wt. %, preferably between about 5.0 andabout 50 wt. %, with respect to initiator. The most preferred amount ofsurfactant which achieves the highest dispersibility of coprecipitatedinitiator in water and minimum coprecipitate particle size is betweenabout 10 wt. % and about 30 wt. % surfactant per weight of initiator.The surfactant also materially alters the solubility of the initiatorand brings the polymer and initiator into more intimate contact prior tocoprecipitation. Surfactants which have been found particularlybeneficial in minimizing emulsion particle or droplet size in theemulsion product include oxygen or sulfate containing compounds such asN--C₈ to C12 alkyl pyrrolidones, C₁₀ to C₁₄ alkyl sulfates, e.g. sodiumdodecyl sulfate, polyglycerides, ethoxylated alcohols or acids, anethoxylated or propoxylated alkyl phenol containing 6 to 50 alkoxyunits, e.g. average 9 ethoxylated nonyl phenol (Igepal® CO-630) andaverage 40 ethoxylated nonyl phenol (Igepal® CO-890) and mixtures ofthese surfactants.

The polymer which is dissolved in the mutual solvent with the initiatorcan be any homopolymer or copolymer of a C₁ to C₄ alkenyl monomerpolymerized product which includes the polymers of vinyl, propenyl, etc.containing monomers such as N-vinyl pyrrolidone, N-vinyl caprolactam,vinyl acetate, alkyl vinyl ethers, styrene, isoprene, maleic acid,maleic anhydride, lower alkyl acrylates or methacrylates and the like,as well a copolymer or terpolymer involving mixtures of these or othermonomers, such as dialkylaminoalkyl acrylates or methacrylates,butadiene, amides and methacrylamides.

The initiator and polymer are combined in a weight ratio of betweenabout 1:5 and about 1:1.5; a ratio of between about 1:3 and about 1:2.5being preferred. It is to be understood that the polymer dissolved withinitiator in the delivery system can be the homopolymer of only one ofthe monomers subsequently employed in a copolymerization process or itcan be the copolymeric, or terpolymeric product of the reaction. Thus,in the polymerization of N-vinyl pyrrolidone, N-vinyl caprolactam anddimethylaminoethylmethacrylate, the polymer mixed with initiator may bethe homopolymer of vinyl pyrrolidone alone, the homopolymer of vinylcaprolactam alone, the copolymer of vinyl pyrrolidone and vinylcaprolactam or the terpolymeric product of the polymerization reaction.Generally it is preferred that the polymer mixed with initiator in thedelivery system is the product of the polymerization process. The numberaverage molecular weight of the polymer employed in the delivery system,can vary over a wide range, e.g. from about 3,000 to about 1,000,000,more desirably from about 10,000 to about 500,000; however, the polymershould be one which is easily dissolved in the mutual solvent.

The polymer and initiator are dissolved in between about 5 and about 15parts, preferable between about 8 and about 12 parts by weight based oninitiator, of a mutual solvent having a boiling point below 140° C.,most desirably below 90° C. at atmospheric pressure. Suitable solventsinclude the alcohols e.g. methanol, ethanol, isopropanol, butanol,cyclohexanol, hydrocarbons e.g. hexane, cyclohexane, etc., acetone,tetrahydrofuran, methylene ,chloride, ethylacetate, aromatic solvents,e.g. toluene, xylene, mixtures of the above or any other inert,vaporizable solvent capable of dissolving both the initiator .andpolymer in the above mixture. The mixture is formed under ambientconditions of temperature and pressure and, after a uniform solution isobtained, the solvent is removed by evaporation by a stream of nitrogenpurge gas or by spray drying to form coprecipitated initiator/polymermicroparticles. The large amount of initiator employed in thecoprecipitated particles of the present delivery system considerablyaides in providing the intimate contact needed for homogeneousdistribution of the coprecipitated particles. These factors ensurestability in the final initiator feed product produced as an aqueousemulsion of the coprecipitate.

Since certain free radical initiators are temperature sensitive, caremust be taken to ensure that the drying step to remove solvent iscarried out at a temperature at which initiator decomposition does notoccur. This is of particular concern when employing high boiling mutualsolvents, e.g. toluene (b.p. 111° C.) and xylene (b.p. 138° C.). Inthese cases, the solvent is removed under a vacuum such that the dryingtemperature does not exceed about 90° C., preferably not in excess of65° C.

After the solvent has been removed, the low viscosity emulsion of thepresent invention is formed by the addition of from about 5 to about 50parts by weight of water under vigorous agitation. Coprecipitatedparticle droplets containing surfactant of between about 0.01 and about100 micron diameter, preferably between about 0.1 and about 50 microndiameter are thus prepared as a stable emulsion which can then besuitably employed as the initiator feed to a free radical polymerizationreaction and may be introduced at the beginning or gradually throughoutthe ensuing polymerization. The viscosity of the emulsion is such thatthe feed may be easily pumped into the reactor; in this regard aBrookfield viscosity of from about 6,000 cps to about 50,000 cps isdesirable and from about 12,000 to about 30,000 cps is most desirable.

Particularly preferred applications of the presentinitiator/polymer/surfactant emulsion involve the homopolymerization ofN-vinyl pyrrolidone using dimethyl 2,2'-azobis-isobutyrate (WAKO 601)initiator and a polyvinyl pyrrolidone having a number average molecularweight of from about 5,000 to about 600,000 in the emulsified feed orthe copolymerization of N-vinyl pyrrolidone with vinyl ester, acrylate,methacrylate, acrylamide and methacrylamide using2,2'-azobis(2-methylbutyronitrile (VAZO 67) or azodiisobutyronitrile(VAZO 64) as the initiator and the above N-vinyl pyrrolidone homopolymerin the pumpable low viscosity ,emulsified feed to the polymerizationreactor.

The total amount of initiator/polymer/surfactant emulsion used in thepolymerization reaction is within the conventional range of from about0.01 to about 3.5 wt. %, more often from about 0.02 to about 1.5 wt. %,based on initiator to total monomer.

The present initiator delivery system possesses many advantages overthose of the art in that no extraneous compounds are introduced into thepolymerization reaction mixture. The presence of surfactant in the abovecritical range allows high water dispersibility of substantially waterinsoluble initiators in the coprecipitated form and also minimizes theparticle size of the coprecipitated particles in the emulsion. Also, thedilution of the stable coprecipitated particles can be easily regulatedto meet the needs of the reaction and avoid plugging of apparatus.Additionally, the microparticle size droplets in the emulsion ensuresmaximum efficiency of initiator properties.

It is found that the introduction of a coprecipitated initiator-polymerfeed to the polymerization reactor accomplishes additional unexpectedadvantages in addition to providing a narrow, fine particle sizedispersion in water. Such a dispersion provides a uniformly distributedreaction medium resulting in a narrower molecular weight distribution ofthe final polymer product and uniformity in the copolymer backbone.Further, the coprecipitated particles avoids polymer formation in feedlines which has posed line clogging problems in prior processes wherethe initiator is introduced as a solution with monomer. Avoidance ofthis problem assures continuous feed operation without loss of monomeror time to clear lines. Still further, the coprecipitated feed avoidsundesirable affects arising from concentrated zones of initiator leadingto local "hot spots" with consequent loss of temperature control andbranching in the polymeric product. Finally, it is clear that thepresent process provides the most efficient use of initiator in the freeradical polymerization of monomers having olefinic unsaturation.

Having thus generally described the invention, reference is now had tothe following examples which illustrate specific and preferredembodiments but which are not to be construed as limiting to the scopeof the invention as more broadly set forth above and in the appendedclaims.

EXAMPLE 1

To a 20 liter reactor was charged 3077 grams of deionized water, 1033grams of vinylpyrrolidone, 4.6 grams of ammonium hydroxide (28%aqueous), and 0.45 grams of tetrasodium ethylenediamine tetraacetic acid(EDTA). The mixture was purged with nitrogen to remove air whileagitating at 250 rpm's and then heated to 75° C.

In a separate vessel, 3.3 grams of WAKO 601 initiator, 0.33 grams ofIgepal® CO-630 and 9.9 grams poly(N-vinylpyrrolidone), i.e. PVP, havinga K-value of 80 were dissolved in 20 ml of methanol, after which themethanol was removed under vacuum, leaving a solid coprecipitate ofinitiator and polymer. The solid product was finely dispersed in 33grams of water to form an emulsion having a particle size of 6-38microns. The resulting emulsion was then added to the polymerizationreactor at 75° C. with agitation. After 30 minutes, 7535 grams of waterand 2297 grams of vinylpyrrolidone was pumped over a 2 hour period intothe reactor at a rate of 80 ml/hr. and after an additional 30 minutes,another initiator emulsion charge was made. This emulsion, graduallyintroduced over a period of 4 hours, was separately prepared as aboveexcept that 6.8 grams of WAKO 601, 0.68 grams of Igepal® CO-630, 20.4 gof PVP and 68 grams of deionized water were used. The resulting reactionmixture was then held for an additional hour at 75° C. before beingdischarged from the reactor. The resulting PVP solution, in 24.5%polymer concentration, had a K-value of 84.

EXAMPLE 2

To a 20 liter reactor was charged 3077 grams of deionized water, 1033grams of vinylpyrrolidone, 4.6 grams of ammonium hydroxide (28%aqueous), and 0.45 grams of tetrasodium ethylenediamine tetraacetic acid(EDTA). The mixture was purged with nitrogen to remove air whileagitating at 250 rpm's and then heated to 75° C.

In a separate vessel, 2 grams of VAZO 67 initiator, 0.4 grams of Igepal®CO-630 and 6 grams poly(N-vinylpyrrolidone), i.e. PVP, having a K-valueof 80 were dissolved in 20 ml of tetrahydrofuran (THF), after which theTHF was removed under vacuum, leaving a solid coprecipitate of initiatorand polymer. The solid product was finely dispersed in 20 grams of waterto form an emulsion having a particle size of 9-33 microns. Theresulting emulsion was then added to the polymerization reactor at 75°C. with agitation. After 30 minutes, 7535 grams of water and 2297 gramsof vinylpyrrolidone was pumped over a 2 hour period into the reactor ata rate of 80 ml/hr. and after an additional 30 minutes, anotherinitiator emulsion charge was made. This emulsion, gradually introducedover a period of 4 hours, was separately prepared as above except that4.2 grams of VAZO 67, 0..84 grams of Igepal® CO-630, 12.6 g of PVP and42 grams of deionized water were used. The resulting reaction mixturewas then held for an additional hour at 75° C. before being dischargedfrom the reactor. The resulting PVP solution, in 23.8% polymerconcentration, had a K-value of 82.

EXAMPLE 3

To a 20 liter reactor was charged 3077 grams of deionized water, 1033grams of vinylpyrrolidone, 4.6 grams of ammonium hydroxide (28%aqueous), and 0.45 grams of tetrasodium ethylenediamine tetraacetic acid(EDTA). The mixture was purged with nitrogen to remove air whileagitating at 250 rpm's and then heated to 75° C.

In a separate vessel, 1.7 grams of VAZO 64 initiator, a mixture of 0.34grams of N-octyl pyrrolidone and 0.03 grams of sodium dodecyl sulfate in10 grams of water and 5.1 grams poly(N-vinylpyrrolidone), i.e. PVP,having a K-value of 90 were dissolved in 20 ml of acetone, after whichthe acetone was removed under vacuum, leaving a solid coprecipitate ofinitiator and polymer. The solid product was finely dispersed in 10grams of water to form an emulsion having a particle size of 11-42microns. The resulting emulsion was then added to the polymerizationreactor at 75° C. with agitation. After 30 minutes, 7535 grams of waterand 2297 grams of vinylpyrrolidone was pumped over a 2 hour period intothe reactor at a rate of 80 ml/hr. and after an additional 30 minutes,another initiator emulsion charge was made. This emulsion, graduallyintroduced over a period of 4 hours, was separately prepared as aboveexcept that 3.8 grams of VAZO 64, 0.76 grams of N-octyl pyrrolidone,0.08 grams of sodium dodecyl sulfate, 11.4 g of PVP and 46 grams ofdeionized water were used. The resulting reaction mixture was then heldfor an additional hour at 75° C. before being discharged from thereactor. The resulting PVP solution, in 21% polymer concentration, had aK-value of 97.

EXAMPLE 4

To a 20 liter reactor was charged 3077 grams of deionized water, 1033grams of vinylpyrrolidone, 4.6 grams of ammonium hydroxide (28%aqueous), and 0.45 grams of tetrasodium ethylenediamine tetraacetic acid(EDTA). The mixture was purged with nitrogen to remove air whileagitating at 250 rpm's and then heated to 100° C.

In a separate vessel, 5.5 grams of VAZO 52 initiator, 1.65 grams ofIgepal® CO-890 and 20 grams poly(N-vinylpyrrolidone), i.e. PVP, having aK-value of 60 were dissolved in 20 ml of methanol, after which themethanol was removed under vacuum, leaving a solid coprecipitate ofinitiator and polymer. The solid product was finely dispersed in 45grams of water to form a microemulsion having a particle size of 5-41microns. The resulting emulsion was then added to the polymerizationreactor at 75° C. with agitation. After 30 minutes, 7535 grams of waterand 2297 grams of vinylpyrrolidone was pumped over a 2 hour period intothe reactor at a rate of 80 ml/hr. and after an additional 30 minutes,another initiator emulsion charge was made. This emulsion, graduallyintroduced over a period of 4 hours, was separately prepared as aboveexcept that 1.9 grams of VAZO 52, 0.57 grams of Igepal® CO-890, 7.5 g ofPVP and 18 grams of deionized water were used. The resulting reactionmixture was then held for an additional hour at 100° C. before beingdischarged from the reactor. The resulting PVP solution, in 22.9%polymer concentration, had a K-value of 63.

While the invention has been described with particular reference tocertain embodiments thereof, it will be understood that changes andmodifications may be made which are within the skill of the art and thescope of this invention.

What is claimed is:
 1. A stable free radical delivery system for a freeradical polymerization of a monomer containing olefinic unsaturationwhich comprises: a pumpable aqueous emulsion of from 0.01 to 100 microndiameter coprecipitated microparticles of a water insoluble free radicalinitiator with a polymer having a number average molecular weight ofbetween 3,000 and 1,000,000 derived from a monomer having olefinicunsaturation combined in a weight ratio of between about 1:5 and about1:1.5.
 2. The delivery system of claim 1 which additionally containsbetween about 1 and about 100 wt. % of an oxygen- or sulfate- containingsurfactant based on initiator.
 3. The delivery system of claim 2 whichcontains between about 5 and about 50 wt. % of said surfactant based onsaid initiator.
 4. The delivery system of claim 1 wherein the weightratio of initiator to polymer in the coprecipitate is between about 1:3and about 1:2.5.
 5. The delivery system of claim 1 wherein thecoprecipitated microparticles have a diameter of from about 0.1 to about50 microns.
 6. The delivery system of claim 2 wherein the surfactant isan ethoxylated C₈ to C12 alkyl phenol.
 7. The delivery system of claim 6wherein the number average molecular weight of said polymer is betweenabout 10,000 and about 500,000.
 8. The delivery system of claim 1 whichcontains between about 5 and about 50 parts by weight of water.
 9. Thedelivery system of claim 1 having a Brookfield viscosity of from about6,000 to about 50,000 cps.
 10. The delivery system of claim 1 for thepolymerization of an N-vinyl lactam wherein the polymer in the deliverysystem is a corresponding vinyl lactam polymer.
 11. The delivery systemof claim 1 wherein the amount of surfactant is between about 5 and about50 wt. % based on initiator.